How Drawing Review Caught an Unsupported Roof Condenser

A 5,000-lb Roof Condenser With No Support Detail

An owner's rep was reviewing construction documents for two hotels in Nashville. The roof carried a condensing-unit array the mechanical sheets sized at about 5,000 lb. The structural sheets had no support detail under it.

The same condensing unit sat on the electrical plan where the gear and the feeder could not both fit. The emergency generator pad on the civil sheet was smaller than the generator the electrical one-line called for.

Each of those is a field change once the unit is ordered. The owner's rep wanted them on the drawings before CD.

Helonic Found a 5,000-lb Load With No Steel Under It

They uploaded both PDF sets, 372 pages. Helonic compared the roof equipment weight with the structural details, the condensing unit with the electrical room, and the generator with its pad.

The list was 286 issues. The three that mattered first were the 5,000-lb roof condenser array with no structural support detail, the condensing-unit electrical conflict, and the undersized emergency-generator pad.

The design team added the roof support, moved the electrical gear, and resized the generator pad before CD.

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286 Issues on 372 Pages, $50,000 to $300,000 Kept Out of the Field

The owner's rep treated those three as field change orders in the $50,000 to $300,000 range: a new roof frame after the condenser is set, a rework of the electrical room, and a pad pour that has to be broken out.

Catching them on the PDF set kept that work in the drawings. The rest of the 286 issues were smaller coordination items on the same pages.

CD went out with the support detail, the electrical clearance, and a pad that matched the generator.

Roof equipment with no support detail is a mechanical and structural miss. Across 1,000+ drawing packages Helonic has reviewed, about 8 in 10 had at least one coordination conflict between disciplines. See how often construction projects go over budget.

NEC Article 700, NFPA 110, and the Undersized Generator Pad

Metro Nashville reviews commercial permits under the International Building Code with local amendments. Roof loads, including mechanical equipment, are designed to ASCE 7, which the code references.

A 5,000-lb condenser array is a concentrated load. The roof framing has to be designed for it, with dunnage or a support frame drawn where the unit sits. Without that detail, the steel erector has nothing to build and the unit has nothing to sit on.

Hotel emergency power falls under the National Electrical Code, Article 700 for emergency systems and Article 701 for legally required standby, and under NFPA 110 for the generator installation. The pad has to fit the generator the one-line calls for, with room for maintenance and the fuel system.

Electrical gear also needs its working clearance under NEC 110.26. Equipment drawn into the same footprint means one of them moves, and moving gear after the feeders are pulled is the expensive version.

“The 5,000-lb condenser had no steel under it, the condensing unit fought the electrical gear, and the generator pad was too small. Those are $50,000 to $300,000 change orders if they wait for the field.”

Nashville Hotel Drawing Review: Questions and Answers